The disclosure of Japanese Patent Application No. 2000-082312 filed on Mar. 23, 2000, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a fuel pressure control apparatus of an internal combustion engine.
2. Description of Related Art
Generally, in an internal combustion engine of the type in which fuel is directly injected into a combustion chamber, the fuel supplied to a fuel injection valve or valves is pressurized by a high-pressure fuel pump, so that the fuel pressure is increased to a value (target value) that permits fuel injection against the pressure in the combustion chamber. The fuel pressure is thus controlled by driving the high-pressure fuel pump in a controlled manner based on a controlled variable that is calculated based on the actual fuel pressure in a fuel pipe and a target value thereof, and by controlling the amount of fuel delivered from the pump in a feedback fashion so that the actual fuel pressure approaches the target value.
The aforementioned controlled variable used in the control in driving the high-pressure fuel pump is calculated based on an integral term that is updated in accordance with a difference between an actual fuel pressure and a target value thereof, a proportional term that is increased or decreased so as to make the difference between the actual fuel pressure and the target value equal to xe2x80x9c0xe2x80x9d. If this controlled variable increases, the amount of fuel delivered from the high-pressure fuel pump increases, resulting in an increase, in the fuel pressure. Conversely, if the controlled variable decreases, the amount of fuel delivered from the high-pressure fuel pump decreases, resulting in a decrease in the fuel pressure.
If the actual fuel pressure becomes excessively higher than the target value, both the integral term and the proportional term are reduced so as to reduce the actual fuel pressure down to the target value. However, since it takes substantial time to reduce the fuel pressure, the integral term becomes excessively small before the actual fuel pressure is reduced down to the target pressure. If the integral term becomes excessively small, the actual fuel pressure cannot be kept at the target value after being reduced to the target value. As a result, the fuel pressure is further reduced, thereby causing so-called xe2x80x9cundershootxe2x80x9d.
In view of the above problem, it has been proposed to inhibit updating of the integral term if the actual fuel pressure becomes excessively higher than a target value, as in a fuel pressure control apparatus as disclosed in, for example, Japanese laid-open Patent Publication No. 6-137199. In this case, the integral term is prevented from becoming excessively small when the actual fuel pressure is reduced to the target value, and thus the undershoot as mentioned above can be prevented.
When the fuel pressure is at a low level even though the required amount of fuel injection is large, for example, at the time of a start of the internal combustion engine, the amount of fuel delivered from the high-pressure fuel pump is set to a value close to or equal to the maximum value so as to promptly raise the fuel pressure to the target value. In this case, even if the integral term is increased so as to raise the fuel pressure, the amount of fuel delivered does not further increase, and therefore the fuel pressure does not rise rapidly. In that case, the integral term tends to be an excessively large value.
Although the integral term starts decreasing after the actual fuel pressure exceeds the target value, the integral term decreases at a low rate or speed. Therefore, the controlled variable used for controlling the amount of fuel delivered from the high-pressure fuel pump, which is obtained after the actual fuel pressure reaches the target value, deviates from the required value in such a direction as to increase the amount of fuel delivered, because of the excessively increased integral term. As a result, the actual fuel pressure exceeds the target value to an excessively large extent, namely, so-called xe2x80x9covershootxe2x80x9d occurs, resulting in a problem such as deterioration of the combustion state of the internal combustion engine.
It is therefore an object of the invention to provide a fuel pressure control apparatus of an internal combustion engine, which is capable of substantially preventing the actual fuel pressure from excessively increasing above a target value due to an excessive increase in the integral term during the time in which the amount of fuel delivered from a fuel pump is approximate to or equal to the maximum value.
To accomplish the above and/or other objects, the invention provides a fuel pressure control apparatus for controlling a pressure of, a fuel that is delivered from a fuel pump to a fuel pipe in an internal combustion engine of a vehicle. A controller of the fuel pressure control apparatus calculates a controlled variable based on at least an integral term that is updated in accordance with a difference between an actual fuel pressure in the fuel pipe and a target value thereof, and controls an amount of the fuel delivered from the fuel pump in a feedback manner, using the controlled variable, so that the actual fuel pressure approaches the target value. The controller inhibits updating of the integral term to a value that results in an increase in the amount of the fuel delivered from the fuel pump, when the amount of the fuel delivered is approximate to or equal to a maximum value thereof.
When the amount of fuel delivered from the fuel pump is approximate to or equal to the maximum value, for example, at the time of a start of the engine, the fuel pressure is not rapidly increased even if the integral term is updated so as to increase the fuel pressure to the target value. Accordingly, the integral term may be undesirably changed (i.e., increased) to an excessively large value that causes an increase in the amount of fuel delivered. With the above arrangement of the invention, however, the upgrading of the integral term in a direction as to increase the amount of fuel delivered is inhibited when the amount of fuel delivered from the fuel pump is close to or equal to the maximum value, and therefore the integral term is prevented from being excessively changed or increased to an excessively large value that causes an increase in the amount of fuel delivered. It is thus possible to suppress or avoid so-called xe2x80x9covershootxe2x80x9d that would otherwise occur when the actual fuel pressure increases to a great extent above the target value due to the excessively increased integral term that had been updated while the amount of fuel delivered from the fuel pump was close to or equal to the maximum value.
In one preferred embodiment of the invention, the updating of the integral term to a value that results in an increase in the amount of the fuel delivered from the fuel pump is inhibited at least when the amount of the fuel delivered becomes approximate to or equal to the maximum value while the actual fuel pressure is increasing toward the target value.
While the actual pressure of the fuel supplied to fuel injection valves is increasing toward the target value in the conventional apparatus, the integral term is in the course of being gradually upgraded to values that will increase the amount of fuel delivered from the fuel pump. With the arrangement of the above preferred embodiment, when the amount of the fuel delivered from the fuel pump almost reaches the maximum value, the integral term is inhibited from being updated to values that will increase the amount of fuel delivered. Thus, the integral term is appropriately prevented from changing to an excessively large extent thereby to undesirably increase the amount of the fuel delivered when the actual fuel pressure reaches and exceeds the target value.
In another preferred embodiment of the invention, the integral term is reset to a value that results in a decrease in the amount of the fuel delivered from the fuel pump, when the updating of the integral term starts being inhibited.
With the above arrangement, the integral term is not only inhibited from being updated to larger values that will increase the amount of fuel delivered from the fuel pump when the amount of delivered fuel almost reaches the maximum value, but also is positively updated or reset to a smaller value that will reduce the amount of fuel delivered. It is therefore possible to further appropriately prevent the integral term from excessively changing in a direction as to increase the amount of fuel delivered.